Embryonic differentiation of sexual dimorphism in vasotocin and mesotocin levels in chickens

Chicken embryos of both sexes were injected on the tenth day of incubation with either estradiol benzoate (EB), aromatase inhibitor [1,4,6-androstatrien-3, 17-dione (ATD)], antiestrogen [tamoxifen (TAM)], antiandrogen [flutamide (FLU)], or the oil vehicle as control (C). At adulthood, at the age of 26 weeks, 10 chickens of each sex were killed and the amounts of immunoreactive arginine vasotocin (AVT) and mesotocin (MT) in the anterior hypothalamus (AHA), posterior hypothalamus (PHA), neurohypophysis (NHP), and pineal gland (PNL) were determined. Control hens had significantly more AVT in PNL and less MT in AHA and NHP than the corresponding roosters. This sexual dimorphism was affected by the embryonic treatments; TAM increased AVT in AHA of cockerels but not of hens. In both sexes, TAM and FLU increased AVT content in NYP. In males, but not in females, ATD also increased AVT content in the NHP. TAM and FLU administration to the female embryo reduced PNL AVT to the amount present in normal males. None of the treatments effected AHA MT in hens, while in cockerels TAM increased it. In females, TAM and FLU significantly increased NHP MT to the level of C males. In roosters, ATD, TAM, and FLU increased NHP MT further. In hens, but not roosters, FLU reduced MT in PNL. These results indicate that embryonic differentiation of the MT and AVT systems is affected by gonadal steroids in chickens.